Apparatus for cooking an egg using microwave radiation

ABSTRACT

The invention relates to an apparatus for boiling an egg, comprising a device for providing microwave radiation in a confined space, comprising a holder with at least one cavity adapted to the shape of an egg with an eggshell, said cavity provided with a first layer surrounding the eggshell, said first layer:—is in heat exchanging contact with the shell of the egg;—has a dielectric constant with an imaginary part, ε″, between 20-500 at a temperature between 0° C.-100° C. and at a microwave frequency of 2.45 GHz, and -having a layer thickness d of 1-6 millimetre and varying less than 30% over the egg, or said holder for holding at least one egg assembly adapted for cooking an egg using microwave radiation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of pending U.S. patent application Ser.No. 13/806,467, filed Apr. 12, 2013, which is a U.S. nationalcounterpart application of international application Serial No.PCT/NL2011/050473 filed Jun. 30, 2011, which claims priority to EuropeanApplication No. 10168243.3 filed Jul. 2, 2010. The entire disclosures ofPCT/NL2011/050473 and European Patent Application No. 10168243.3 arehereby incorporated by reference

BACKGROUND

The present invention relates to an apparatus for cooking an egg usingmicrowave radiation.

Preparing an egg by boiling the egg in water of about 100 degreesCelsius usually takes about 3.5-4 minutes for a so called soft-boiledegg, i.e. an egg having solid albumin or egg white and warm butsubstantially liquid yolk. Furthermore, usually the water needs to beheated to the required temperature, which takes additional time. Manymethods and apparatus have been proposed for properly boiling an eggmore swiftly. Some of these methods use microwave radiation. When usinga microwave oven for cooking an egg as such, the egg may explode insidethe oven or, even worse, in the hands or face of the consumer. Thus,methods were devised for cooking an egg in a microwave oven whilepreventing the egg from exploding.

For instance, a method is proposed, in which an egg is first shelled andits contents are put in a small container, in which the egg issubsequently boiled in a conventional microwave oven in about 60seconds. The end result often is a too hard or rubbery albumin. Often,the egg white is not cooked uniformly. In professional kitchens, theresult of this method is not acceptable.

In another known method, the egg in unbroken state is placed in anelectrically conducting holder filled with a small amount of water. Theholder is subsequently placed in a conventional microwave oven. In about4-5 minutes, an egg is cooked. The cooking time is not reduced, but itdoes require less time to boil the water first.

In EP-988795 an egg is placed in a container having walls which aretransparent to microwave radiation. The container is filled with hotwater of 90° C., and placed in a conventional microwave oven.Subsequently, the egg is placed in the container, and boiled in about110 seconds.

In EP-992197, an apparatus is presented, in which an egg is boiled in amicrowave field, while hot water is poured over an egg (shower).

These methods are complicated, and require additional devices or steps,and additional time to heat up the water.

EP-1.917.867 discloses a package for cooking an egg in a microwave oven.The package comprises a covering adapted to surround an egg, and isarranged to partially transmit microwave radiation and partially absorbmicrowave radiation. As an example, a medium sized egg is wrapped in atissue, soaked in 20 ml 0.5M NaCl solution, and a rubber material wasused for packaging. The package was placed in a regular commercialmicrowave oven and subjected to a heating program. This procedure ofpackaging is laborious and does not allow reproducible results, which isin particular important in consumer applications.

JP60126062 discloses a method for preparing an egg in a microwave oven,in which an egg is placed in a container with water containing 5 grsalt. When subjecting this to 500 W microwave radiation, a hard-boiledegg is prepared in about 390 sec. It is suggested that a soft-boiled eggcan be prepared by increasing salt concentration. The suggestedpreparation time is still long, even longer than just preparing an eggin hot or boiling water. Furthermore, it requires the preparation ofsalt water with the right amount of salt added.

SUMMARY OF THE INVENTION

The invention aims to provide a high quality cooked egg usingsubstantially less time for preparation.

The invention further and/or alternatively seeks to provide a modifiedegg which allows for instance a consumer to cook the egg in a shorttime.

According to a first aspect of the invention this is realized with anapparatus for boiling an egg, said apparatus comprising a device forproviding microwave radiation in a confined space, said space furthercomprising a holder provided with at least one cavity adapted to theshape of an egg with an eggshell,

said cavity provided with a first layer surrounding the eggshell, saidfirst layer:

-   -   is in heat exchanging contact with the shell of the egg;    -   has a dielectric constant with an imaginary part, ε″, between        20-500 at a temperature between 0° C.-100° C. and at a microwave        frequency of 2.45 GHz, and    -   having a layer thickness d of 1-6 millimetre and varying less        than 30% over the egg, or

said holder for holding at least one the egg assembly comprising an eggwith an eggshell which is provided with a packaging surrounding theeggshell, said packaging comprising a first layer which enfolds theshell of the egg and is in heat exchanging contact with the shell of theegg, has a dielectric constant with an imaginary part, ε″, between20-500 at a temperature between 0° C.-100° C. and at a microwavefrequency of 2.45 GHz, and has a layer thickness d of 1-6 millimetre andvarying less than 30%, and said packaging designed to retain the layerthickness of said first layer while said egg assembly is subjected tosaid microwave radiation to become a boiled egg.

The apparatus can for instance be designed to prepare one or severaleggs at the same time. It allows easy preparation of eggs fast, and withminimal use of energy and waste material. In an embodiment, theapparatus comprises a device for measuring the weight of an egg in acavity.

The invention further provides a method for cooking an egg usingmicrowave radiation, said method comprising the steps of providing anegg assembly according to the preceding definition, positioning said eggassembly in a space enclosed with substantially microwave-reflectingwalls, and subjecting said egg assembly in said space to an amount ofmicrowave radiation common for household microwave oven during 30-180seconds.

The invention further provides an egg packaging for providing an eggassembly as defined above, said egg packaging comprising a layer ofpolymer material having a softening temperature of above 130° C., saidlayer having a inner surface following the contour of an egg, andenclosing an egg completely and liquid tight, said layer furthercomprising spacers extending from said inner surface for keeping an eggin the centre of the packaging with its shell at about 1-10 mm from theinner surface, and said packaging further comprising a filling opening,allowing the space between an egg and the inner surface to be filledwith a liquid.

The current invention allows a so-called soft-boiled egg to be preparedwithin 180 second. In particular, it allows a soft-boiled egg to beprepared within 120 seconds. This preparation time refers to an averagesize chicken egg. Usually, a chicken egg will be between about 45-75 gr.A relatively small egg may take shorter time to be prepared, and arelatively large egg can take relatively longer time. The inventionallows preparation of an egg with minimal use of energy, without wastingwater, and in such a way that a consumer can use it.

In the invention, the properties of the layer are defined with respectto a boiled or prepared egg. In this context, prepared relates toprocessing an egg in such a way that it becomes a boiled egg. A boiledegg in this context is an egg which usually is anywhere between ahard-boiled egg and a soft-boiled egg. For a soft-boiled egg, an eggusually is prepared in such a way that the albumin is set, in otherwords, the albumin is solid, and the yolk is warm but stillsubstantially liquid. It is of course also possible to use the methodand apparatus for producing at any stage of preparation, for instance anegg with its yolk completely solid or set, i.e. a so-called hard-boiledegg. This usually requires a longer preparation time. The inventionallows an egg to be prepared in such a way that its quality iscomparable to an egg prepared in hot or boiling water. In particular,this “quality” relates to the taste and texture of the prepared egg.

The egg referred to in this document is usually a chicken egg, althoughit is also be possible to boil other hard-shelled eggs using the currentinvention. These eggs may also be prepared in a relatively short time,depending on the type of egg.

Usually, microwave radiation is defined as electromagnetic radiationwith a frequency between 1-100 GHz. In particular, in current microwaveovens, the microwave radiation has a means frequency of about 1-10 GHz.In current household microwave ovens, the radiation is about 2-3 GHz. Inparticular, the microwave radiation allowed in most countries has afrequency of about 2.45 GHz. In this respect, it should be clear thatthe egg assembly of the current invention comprises a layer with certainproperties which are defined at a specific microwave frequency. The eggassembly can, however, also be subjected to microwave frequencies atother ranges in order to obtain a prepared egg. Usually, as 2.45 GHz isan accepted frequency for microwave radiation, that particular radiationis used.

The preparation time depends on the amount of microwave radiation energyto which the egg is exposed. In tests conducted in the currentinvention, a standard microwave oven was used. This type of microwaveovens supply microwave energy, as explained above. The amount ofmicrowave power supplied is usually expressed in Watt. Most microwaveovens supply a maximum of about 1000-1200 Watts of microwave radiation.In current microwave ovens, the supplied energy can be set to parts ofthis maximum energy per time. Furthermore, usually the time can be set,in this way the total amount of energy supplied to (usually) a foodproduct in the microwave oven. In the current invention, an egg can besubjected to microwave radiation. In an embodiment, the egg is subjectedto microwave radiation having a frequency as referred to above. It is,for instance, conceivable that a specific device is made in which one ormore eggs are prepared simultaneously. In this device, the microwaveradiation can have any one of the frequencies mentioned above. Usingsuch a specific device allows several eggs to be prepared at the sametime, but having different preparation settings, allowing for instance asoft-boiled and a hard-boiled egg to be prepared at the same time. Itmay even be possible to prepare these different eggs in the samepreparation time.

The alternating electromagnetic field generated inside the microwaveoven leads to excitation, rotation/collision of polar molecules and ionsinside the food. These molecular frictions generate heat andsubsequently lead to temperature rise. Two major mechanisms, dipolar andionic interactions, are responsible for heat generation inside thefoodstuffs. In case of dipolar interaction, polar molecules such aswater molecules inside the food rotate according to the alternatingelectromagnetic field. The water molecule is a “dipole” and these“dipoles” will orient themselves when they are subject to anelectromagnetic field. The rotation of water molecules will generateheat for cooking. In case of ionic interaction, in addition to thedipole water molecules, ionic compounds (i.e. dissolved salts) in foodcan also be accelerated by the electromagnetic field and collided withother molecules to produce heat. Therefore, the composition of a foodand packaging will affect the rate and uniformity of heating inside themicrowave oven. Food with higher moisture content will be heated upfaster because of the dipolar interaction. Also, when the concentrationof ions, e.g. dissolved salts, increases, the rate of heating alsoincreases because of the ionic interaction with microwaves.

In order to account for the various heating mechanisms (termed lossmechanisms), the dielectric constant for a real dielectric attains acomplex form

ε*=ε″+·ε″

The imaginary part ε″ is termed the effective loss factor, and accountsfor dipolar relaxation loss as well as conduction (and also forMaxwell-Wagner losses, which are important only at lower frequencies).In general, ε″ is a function of the temperature, the composition andmoisture content of a material, and the distribution of the electricfield in the material and in the microwave oven. In the currentinvention, ε″ may be defined by using subscripts in which i is thetemperature and j the frequency of the microwave radiation. Thus,ε″_(60° C. 2.45 GHz) refers to the value of ε″ of a substance at atemperature of 60° C. and at a microwave frequency of 2.45 GHz. Thus, inthe current context, it does not mean that the material is only to besubjected to those conditions, but that the material has a certain ε″value at that specified temperature and that specified frequency.

In this invention, the packaging may be a more or less permanentenvelope enclosing the egg. Thus, after preparation the packaging mustbe broken or removed together with the egg shell in order to use or eatthe boiled egg. The packaging may be provided with measures whichfacilitate removal. Thus, the packaging may be provided with a weakeningline allowing removal of for instance the top of the packaging. In anembodiment, the first layer has a combination of layer thickness d andε″ selected from the area bounded by the curves:

ε″(d)=229.d ⁻¹ ¹⁶⁸, ε″(d)=2989.d< ² ²³⁷ and ε″(d)=300

for an egg of between 45 and 75 gr, allowing said egg to become a boiledegg in less than about 120 s when subjected to microwave radiation.Experiments showed that in fact the combination of material property andlayer thickness provided the right condition for preparing an egg inmicrowave radiation. In fact, the ε″ in this embodiment is the averagevalue of ε″ during the boiling process. In practice, it will almostequal the value of ε″ at 60° C. Again, this ε″ is defined at 2.45 GHz.

The packaging of the invention comprises a first layer and is designedto retain the layer thickness of said first layer while said eggassembly is subjected to said microwave radiation to become a boiledegg. To that end, in an embodiment the first layer may be heat resistantsuch that it does not deform at a temperature of up to about 130° C.Alternatively, the packaging may comprise an outer layer which enfoldsthe first layer and which does not deform at a temperature of up toabout 130° C. The outer layer may further be water tight. In anembodiment, the outer layer is a polymer layer. In an embodiment theouter layer is less than 2 mm thick. Such a layer can for instance befrom polypropylene (PP), PET, of a similar plastic material.

A suitable material for a layer of the packaging is salt water. Forinstance, the layer may comprise a saline solution of water confined ina thin layer of packaging material holding the saline solution of waterin a defined layer around an egg. Alternatively, a matrix material mayhold the water. For instance a fibrous materials can be used for waterretention and mechanical stability of the packaging as an embodiment ofthis invention.

In an embodiment, the first layer comprises solid materials which retaintheir layer thickness during boiling of the egg. For instance, suchmaterials as clays and (hydro-) gels, possessing the dielectricproperties claimed above, and making a firm thermal contact with an egg.An example of such a gel material is polyacrylamide gels (PAAM) knownfor their mechanical stability up to temperatures of about 230° C., andhaving ε″ in the range of 10-200 when ions are added. In an embodiment,polyacrylamide gel (PAAM) doped with K₂CO₃ or Na₂CO₃ can be used.

In an embodiment, aqueous solutions of salts other than NaCl can be usedin the packaging to achieve the same results, provided that thedielectric properties and thickness of the packaging layer are in theranges covered by this invention.

The first layer can be part of a layer assembly enveloping the egg. Thelayer assembly in that embodiment comprises a contact layer positionedbetween the first layer and an egg shell. The contact layer is flexiblein order to follow the shape of the egg. It further allows a heatexchanging contact between the first layer and the egg shell. In anembodiment, it is microwave transparent. Furthermore, it is heat stableup to at least 130° C. The invention further relates to a method forcooking an egg, comprising the steps of:

-   -   providing said egg with a layer which envelops said egg, which        layer is in heat exchanging contact with the shell of the egg,        has a dielectric constant with an imaginary part, ε″, between        20-500 at a temperature between 0° C.-100° C. and at a microwave        frequency of 2.45 GHz, and which layer has a layer thickness d        of about 1-6 millimetre;    -   determining a weight of said egg;    -   based on said weight and based on said layer properties and a        desired cooking grade of said egg, determining cooking        parameters based upon microwave energy and cooking time;    -   subjecting said enclosed egg to microwave radiation;    -   determining during said cooking the temperature of the egg at        various moments;    -   adjusting a cooking time or an energy of said microwave based        upon the determined temperature values.

The layer can for instance be provided by placing the egg in anapparatus as described above. The weight can be determined. Equivalentto that, the volume can be determined for instance and this value can beused. The determined temperature can be used, for instance, to calculatethe absorbed energy. Thus, the additional energy needed to prepare theegg in the desired way can be calculated. The additional energy allowscalculation of the additional cooking time and/or microwave energy orthe combination of both. There are other, equivalent control schedulespossible based on this example.

In the method, cooking time can be set as a fixed parameter, oralternatively, the microwave radiation energy or power can be a fixedvalue. The energy can for instance be controlled by switching themicrowave on and off during some seconds when the temperature rises toofast or its value is too high.

The invention further applies to an apparatus comprising one or more ofthe characterizing features described in the description and/or shown inthe attached drawings. The invention further pertains to a methodcomprising one or more of the characterizing features described in thedescription and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order toprovide additional advantages. Furthermore, some of the features canform the basis for one or more divisional applications

DESCRIPTION OF THE DRAWINGS

The invention will further be elucidated, referring to an embodiment ofan egg assembly and a packaging for an egg shown in the attacheddrawings, showing in:

FIG. 1 a cross section of an egg with enfolding layer;

FIG. 2 a longitudinal cross section of an egg with alternativeenveloping layer, and

FIG. 3 a transverse cross section of the egg of FIG. 2

FIG. 4 a graph showing the effect of weight of an egg, and layerparameters;

FIG. 5 a graph showing the ε″ of salt water as a function oftemperature;

FIG. 6 a drawing of an apparatus for preparing an egg;

FIG. 7 a schematic side view of an embodiment of a holder for theapparatus of FIG. 6.

DETAILED DESCRIPTION OF EMBODIMENTS

In FIG. 1, a cross section through an egg assembly adapted to beprepared in a conventional microwave oven is shown. The egg 1 has a yolk2, albumin 3, and a shell 4. Enclosing the shell, the egg is providedwith a packaging which in this embodiment consists of a single layer 5which completely enfolds the egg 1. This layer 5 is here in a firmthermal contact with the shell 4. In order to prevent an egg fromexploding while subjected to microwave radiation, and at the same timeallowing swift preparation of an egg, it was found that the layer whichis in contact with the egg shell should have a dielectric constant withan imaginary part, ε″, in a certain range, explained below.

In an embodiment, the layer 5 can comprise a layer of water-retainingmatrix material. An example of such a matrix material is a fibrous layercapable of absorbing water. Other examples of such matrix material are ahydrogel, for instance. The layer 5 is such that when soaked with waterit results in a layer with the thickness of about 1-5 mm. In anembodiment, such a layer is soaked with salt water containing 0.4-0.5 MNaCl.

In an alternative embodiment, the layer comprises a water-retainingmatrix material holding a salt, for instance NaCl, in a substantiallysolid form. In a layer of between 1-5 mm of water-retaining material,about I gr of salt will generally be present. In an embodiment, the saltwill be uniformly distributed. Before use, an egg with such a layer isto first brought into contact with some water which it will soak. Next,it is placed in a microwave oven and prepared. The matrix material orany material enclosing it should be such that the layer thicknessremains almost the same during the boiling process.

In order to maintain the properties of layer 5, the packaging cancomprise a further, outer layer (not shown in the drawing). To that end,the outer layer can have one of the following properties. It can bedesigned to retain the thickness of the layer 5 during boiling of theegg. If the layer 5 comprises a water retaining matrix material, it canalso be a watertight layer in order to prevent the water to escapeduring boiling of the egg. In an embodiment, the outer layer is aplastic material enfolding the layer 5 and having a thickness of lessthan 2 mm.

Alternatively or additionally, in order to diminish influences of thefirst layer on the egg, for instance its taste, a contact layer can bepresent between the egg shell and the first layer. Via this contactlayer, the first layer is in heat exchanging contact with the egg shell.The contact layer prevents the first layer, or (salt) water or othercomponents in the first layer, to come into direct contact the eggshell. The contact layer in an embodiment is an elastomeric layerfollowing the shape of the egg it encloses. It thus allows thermalcontact between the first layer and the egg shell.

In FIGS. 2 and 3, an alternative way of providing a layer around an egg,which allows preparation of an egg using microwave radiation, is shown.This embodiment provides a packaging for an egg. In this embodiment, thepackaging provides a layer 6 of material. This layer 6 is shaped to havean inner surface following the contour of the shell 4 of the egg. Thissurface is at a distance from the eggshell of the egg. Thus, it allowsthe provision of a uniform cavity 8 around the shell 4 of the egg. Inorder to provide a uniform cavity, i.e. to make the distance between theinner surface of the layer 6 and the outer surface of the shell 4 of theegg as uniform as possible, the packaging is provided with spacers 7 onthe layer 6. These spacers 7 keep an egg substantially centred in thepackaging, thus providing a substantially uniform cavity 8 around theshell 4 of the egg. In use, the cavity can be filled with a materialwhich has the properties defined above. In an embodiment, the packaginghas two parts which are connected via a hinge 9. Thus, the packaging canbe hinged open, an egg can be placed in the packaging, and the packagingcan be closed around the egg. Filling opening 10 is shown in thedrawing. In an embodiment, a closed rim 11 (FIG. 3) provides aliquid-tight closure of the packaging. In a further embodiment, a partof the closing rim 11 can provide a sealable conduit with a fillingopening 10 for filling the uniform cavity 8 with a liquid having theproperties, in particular the imaginary dielectric constant, describedabove.

In an embodiment, the packaging is substantially made from a polymermaterial having a softening temperature of at least 130 degrees Celsius.An example of such a polymer material is PET, polyethyleneterephthalate. In such an embodiment, the packaging can be formed from asheet of this polymer material in a deep-drawing process. The latterprocess as such is well known in the art, and will not be explainedfurther in this description. In such an embodiment, a hinge may beformed as a thinned line of material, allowing two parts to hinge. Itthus forms a living hinge. In a particular embodiment, the spacers 7 maybe formed as parts of the layer of polymer material which bulges inward.

In operation, such a packaging is opened, an egg is placed inside, andthe packaging is closed again. Next, via a sealable filling opening thecavity 8 is filled with a liquid material having the propertiesdescribed in this document. In an embodiment, the distance between theinner surface of the layer and the egg shell 4, i.e. the width of thecavity, is between about 2-4 mm, in particular about 3 mm. This cavitycan be filled with a liquid having a dielectric constant with theimaginary part mentioned above. As an example, it can be filled withwater having about 0.4-0.5 M NaCl. This packaging thus prepared can beplaced in an ordinary household microwave oven. Next for preparing asoft-boiled egg, this is subjected to a program for instance of 70seconds at 800 Watt and about 20 seconds at 560 Watt. Thus, it ispossible to prepare a soft-boiled egg in about 80 seconds.

In the current invention, it was found that in order to prepare an eggin microwave radiation, it requires a packaging comprising a first layerhaving certain well defined properties. It was found that the rightproperties of this layer prevent the egg from exploding in a microwaveoven. In fact, it was found that the relation between layer thicknessand ε″, the imaginary part of the dielectric constant, is of importance.FIG. 4 shows the results of calculations giving the upper range andlower range of the relationship between ε″ and layer thickness for whichit is possible to prepare an egg using microwave radiation. Please notethat the value of ε″ in the graph is defined at 2.45 GHz. In fact, thearea between these curves is the area in which ε″ and layer thickness dshould be in order to allow a chicken egg of between about 45 gr and 75gr to be prepared within 120 seconds. Within this area, for instance amaterial with a certain ε″ can be linked to a layer thickness. In fact,the lower limit relates to the combinations of ε″ and layer thicknesswhich is close to the properties which allow a 45 chicken gr egg to behard-boiled in about 100 seconds. The upper limit relates to thecombinations of ε″ and layer thickness which little above to theproperties which allow a 75 gr chicken egg to be soft-boiled in about120 seconds. In equations, the lower limit can be represented byε″(d)=229.d^(-1.168) and the upper limit can be represented byε″(d)=2989.d^(-2.237). The area is further limited by, ε″(d)=300.

In fact, it was found that a 45 gr egg, for instance a small chickenegg, can be soft-boiled in about 80 seconds when layer 5 has a layerthickness d and ε″ selected from an area with a lower limitε″(d)=380.d^(-1.25) and the upper limit can be represented byε″(d)=1600.d⁻². In this range, ε″(d)<300. On the other hand, a 75 gregg, for instance a large chicken egg, can be soft-boiled in about 120seconds when the layer thickness d and ε″ selected from an area with alower limit ε″(d)=1600.d⁻² and the upper limit can be represented byε″(d)=2989.d^(-2.237). In this range, ε″(d)=300 again limits the area.

FIG. 5 shows a curve indicating the relationship between temperature, ε″and molarity of salt or saline water, i.e. water having the indicatedmolarity of NaCl. It shows that the relationship between temperature, ε″and molarity is complex and non-linear. It thus illustrates that it isnot straight forward to transfer one molarity into another.

In practice, when providing egg assemblies according to the invention tothe consumer, the effectiveness of the assembly may be further improvedby a proper matching between size (or better yet, weight) of the egg, ε″of the material provided in the packaging, and layer thickness of thepackaging. Furthermore, the layer thickness should vary less than 30%.In that way, it can be possible to provide egg assemblies which can be“boiled” in for instance a microwave oven in a reproducibly way.

FIG. 6 shows a schematic drawing of an apparatus for cooking or boilingor preparing an egg. The apparatus 21 has a housing 22 which has acavity 23. In this cavity 23 a holder 24 is provided. This holder 24 hasat least one cavity 25 in the shape of an egg. In this embodiment, thereare two cavities 25. In an apparatus there can be as many as 4 cavities25 for preparing eggs. The holder 24 provides the layer described above.

The apparatus 21 further has a controller 26 which is operationallycoupled to a weight sensor 27 in each of the cavities 25 for determiningif an egg is placed in one of the cavities 25. In particular if an eggis placed in one of the cavities 25, it allows for determining itsweight. Alternatively, one weight sensor 27 can be provided weightingincrease in the weight of the holder 24. As the eggs have about the sameweight, it allows determination of the number of eggs in the holder 24.Providing a weight sensor 27 for each of the cavities 25 has anadditional advantage in that it allows detection of which of thecavities 25 holds an egg.

The controller is in a further embodiment operationally coupled to atemperature sensor 28 in each of the cavities 25. The temperature sensor28 first is a safety for preventing overheating of the egg(s).Furthermore, it provides temperature information to the controller 26during the preparation process for controlling the preparation process.Finally, it measures the temperature of an egg before it is going to beprepared. In that way, the process can be controlled better. Thetemperature sensor 28 in an embodiment is positioned to contact an eggplaced in the cavity 25.

In an embodiment, the apparatus 21 has an inlet 29 for water. In anembodiment, this inlet 29 is attached to a water mains. The inlet 29 inthis embodiment is provided with a controllable valve 30 which isoperationally coupled to the controller 26. In that way, the controller26 can arrange for the provision of water in the holder 24. In anembodiment, a further temperature sensor 32 is provided in the inlet 29for measuring the temperature of incoming water. This water can forinstance also be used for cooling an egg after the cooking process.

In a further embodiment, the apparatus 21 has an outlet 31 for water. Inan embodiment, this outlet 31 is coupled to a drain. The outlet 31 inthis embodiment is provided with a controllable valve 38 which isoperationally coupled to the controller 26. In that way, the controller26 can arrange for removal from holder 24 of the water after use.

In an embodiment, the apparatus further has a input part 33 throughwhich the desired state of preparation of the egg can be entered. Thisinput part 33 is operationally coupled to the controller 26. Forinstance, a selection switch 35, knob, or push button 35 can be providedwhich has several settings, for instance three settings for selecting asoft, medium or hardboiled egg. Display 34 is operationally coupled tothe controller 26 and can display for instance settings of selectormeans 35, but also remaining preparation time. Furthermore, theapparatus can sound an alarm when the eggs are ready.

In the embodiment, the housing has hinges 36 for a lid 37, enablingopening of the microwave cavity 23. The holder 24 in this embodiment hastwo parts thus allowing access to the cavities 25 in order to place orremove eggs.

Based on the weight, measured temperatures and selection on the inputpart 33, the controller sets the amount of microwave energy needed toprepare egg in the desired way.

Controller 26 may also calculate a preparation time. Furthermore, theapparatus 21 can have display 34 showing for instance the remaining timefor preparing the one or more eggs in the holder 4.

In operation, lid 37 is opened providing access to the holder 24. Forinstance hinging the two parts of holder 24 apart provides access to thecavities 25. Next, eggs can be placed in the cavities 25. The holder 24and the lid 37 are closed, and a user operates selection switch 35 inorder to set the way the eggs need to be boiled. The controller 26operates the valve 30 to allow water via inlet 29 to access the holder24. The holder 24 is further provided with for instance salt in a matrixin order to be mixed into the water to provide the first layer havingthe parameters required. It will be clear that said first layer being inheat exchanging contact also means that a thin layer of material whichis transparent to microwave radiation, or almost transparent tomicrowave radiation, can be present between the first layer and the eggshell. Thus, holder 4 can be a hollow material having a space whichprovides, when filled with salt water as defined above, the firsts layerinside holder 4, enveloping or enfolding the egg, and in heat exchangingcontact with said egg. Alternatively, in order to diminish influences onthe egg which may influence taste, a contact layer, also discussedabove, can be present between the egg shell and the first layer. Viathis contact layer, the first layer is in heat exchanging contact withthe egg shell. The contact layer prevents the first layer, or (salt)water from the first layer, to contact the egg shell.

After or while filling the cavity 25 in the holder 24 with water,controller 26 determines the size of the eggs present, the desiredcooking selection, the temperature of the eggs and the temperature ofthe water. From these parameters controller 26 can be able to calculatethe required microwave power and cooking time. Controller 26 starts thecooking process, in an embodiment meanwhile monitoring the temperatureof the eggs in order to prevent overheating and to follow the process.If required, and in an embodiment, controller 26 can adjust the power ofcooking time depending on measured parameters. Thus, it may be possibleto use eggs that are less strictly selected. Alternatively, demands onthe layer around the eggs can be less strict. Controller 26 can alsodisplay the remaining time on display 34. Using the apparatus, eggs maybe prepared in about 60-180 seconds. It was found that a selection ofM-class eggs would be enough to result in a good preparation result.M-class eggs are selected eggs having a weight of between about 53-63grams. Thus, the apparatus would allow for instance a range of eggs tobe prepared in a reproducible way, even by ordinary consumers. Thus, theapparatus can be designed for preparing M-class eggs.

FIG. 7 shows an embodiment of a holder 24 capable of holding at leastone egg in the apparatus 21. The holder 24 in this embodiment has afirst half 24′ and a second half 24″, allowing access to the egg cavity25. It is clear that other provisions are possible to allow access tothe egg cavity 25. The egg cavity 25 in this embodiment has an ellenclosing layer assembly comprising in this embodiment naturally thefirst layer 5. The layer assembly further comprises a contact layer 40to be positioned between the first layer 5 and the egg.

The layer assembly can further comprise an outer layer 41. In thisembodiment, the layer assembly is positioned in the egg cavity 25 insuch a way that a space 42 remains between the outer layer 41 and theinner wall of the holder 24 defining the egg cavity 25. Surrounding theegg cavity 25 in order to seal it, a sealing ring 43 can be provided.The layer assembly in the egg cavity 25 can be permanently connected tothe holder 24. In an embodiment, it is replaceable. Thus, it can be usedmany times, or alternatively a disposable layer assembly can be used.

The material of the holder 24 is permeable to microwave radiation andabsorbes as little microwave radiation as possible. It can be largelymade from a plastic material. The lyer assembly is held inside the eggcavity 25. Egg cavity 25 is shaped in such a way that every shape of eggin a certain weight class of eggs fitted with the layer assembly fitswithin said egg cavity 25, preferably with little space remaining. Inthe drawing, the remaining space 42 is represented larger than it willusually be.

Contact layer 40 is flexible, in order to be able to follow the shape ofdifferent eggs. In particular, it is rubbery or an elastomeric material.Thus, enclosure of air between the egg shell and the contact layershould be prevented as much as possible. The contact layer 40 preventsliquids from the first layer 5 from contacting an egg held in the layerassembly. The contact layer 40 further allows a heat exchanging contactbetween the first layer 5 and an egg shell of an egg. In order to beable to withstand the temperatures of cooking or preparing an egg, thecontact layer should be heat stable up to a temperature of about 130° C.In an embodiment, the contact layer is a silicone polymer layer, or analternative elastomeric material.

The outer layer in an embodiment is flexible, preferably evenelastomeric, though it may be a little more ridged than the contactlayer 40. It too like the contact layer 40 is transparent to microwaveradiation. It also is stable up to a temperature of about 130° C.

In an embodiment, the first layer 5 provided between the contact layer40 and the outer layer 41 is a layer of salt water described above.Alternatively, it is a hydrogel or another material having theproperties mentioned earlier in this description. In an embodiment, thefirst layer 5 is in contact with the water supply or inlet describedabove.

In an embodiment, via the inlet 29 and using the controllable valve 30,it is possible to add more or less water and thus to modify propertiesof the first layer. It is, for instance, possible to modify the layerthickness for instance by providing more or less water. It is evenpossible to modify in that way the ε″ of the first layer. Thus, usingmeasure weight of each egg, the controller can modify the first layerproperties to allow preparation of an egg within the short time definedabove.

It will also be clear that the above description and drawings areincluded to illustrate some embodiments of the invention, and not tolimit the scope of protection.

Starting from this disclosure, many more embodiments will be evident toa skilled person, which are within the scope of protection, and theessence of this invention and which are obvious combinations of priorart techniques and the disclosure of this patent.

1-14. (canceled)
 15. A method for cooking an egg with an eggshell, bymeans of an apparatus, comprising the steps of: placing at least one eggin a first part of a holder; closing the holder by means of a secondpart of the holder so that the egg is placed in an egg cavity defined bythe parts of the holder; the parts comprising inner surfaces adapted tothe shape of the egg, the inner surfaces follow the contour of the shellof the egg in the egg cavity at a distance thereof of 1-6 millimeter,the distance varies less than 30% over the contour of the shell of theegg and defines a space between the egg in the egg cavity and the innersurfaces of the parts; filling the space between the egg and the innersurfaces of the parts with a liquid through a filling opening in atleast one of the parts, the liquid forming a layer being in heatexchanging contact with the shell of the egg and has a dielectricconstant with an imaginary part, ε″, between 20-500 at a temperaturebetween 0° C. and 100° C. and at a microwave frequency of 2.45 GHz;providing microwave radiation in a confined space in which the holder ismounted; cooking the egg.
 16. A method according to claim 15, comprisingthe steps of: determining a weight of the egg; based on the weight andbased on the layer properties and a desired cooking grade of the egg,determining cooking parameters based upon microwave energy and cookingtime; subjecting the enclosed egg to microwave radiation; determiningduring the cooking temperature of the egg at various moments; adjustinga cooking time or an energy of the microwave based upon the determinedtemperature values.